In recent years, polymer members formed from polymer materials serving as bass materials have been noted as members used for charging, development, transfer, toner supply, and the like in image forming devices, e.g., dry electrophotographic devices, with progress in the electrophotography. The polymer members have been used in the forms of elastic rollers, e.g., charge rollers, development rollers, transfer rollers, and toner supply rollers. A process of charge, transfer, or the like by using such an elastic roller has advantages that, for example, a required image formation member charge potential and a required amount of toner transfer can be achieved at a lower electric source voltage by using the polymer member as compared with known corotron chargers and the like.
The polymer members used for the above-described applications are required to have appropriate electrical resistance values in accordance with their respective applications and to be capable of stably maintaining the electrical resistance values. In particular, it has become required that the range of variation in electrical resistance value is narrow when the use environment conditions (temperature, humidity) are changed or continuous energization is conducted with speedup and colorization of the electrophotography process in recent years. If a wide range of variation in electrical resistance value is exhibited in this case, a poor image tends to be caused due to an occurrence of poor transfer, poor development, poor charge, or the like. Consequently, a good electrophotographic image may not be produced.
On the other hand, examples of general techniques to control the electrical resistance value of a polymer member include (1) a method in which the electrical conductivity is imparted by adding an electrically conductive agent composed of an electrolyte, (2) a method in which the electrical conductivity is imparted by adding an electrically conductive filler, and (3) a method in which the electrical conductivity is imparted by adding a material capable of forming a charge-transfer complex.
In the method (1), among them, various materials, e.g., carbon black and metal oxides, are used as the electrically conductive agent. For the polymer members including these previously known electrically conductive agents, the electrical resistance values tend to increase in a low-temperature and low-humidity environment but the electrical resistance values tend to decrease in a high-temperature and high-humidity environment on the other hand. Furthermore, the electrical resistance values increase when continuous energization is conducted. Therefore, a poor image tends to be caused due to these variations in electrical resistance values, and the above-described requirements related to the stable electrical resistance cannot be satisfied.
With respect to technologies of improving materials used for the above-described electrically conductive polymer members, for example, Patent Document 1 discloses an electrically conductive member including a polymer material prepared by adding an ionic electrically conductive agent to a predetermined polyurethane based polymer serving as a base material, wherein contamination of other members is prevented and variations in electrical resistance due to environmental changes are reduced. Patent Document 2 discloses an electrically conductive member which is used for OA equipment and which includes a composition composed of a predetermined polyurethane and lithium imide, wherein variations in electrical conductivity during continuous energization and due to changes in environmental conditions are reduced. Furthermore, Patent Document 3 discloses an electrically conductive member including an electrically conductive material containing a predetermined polyurethane foam or an elastomer and an electrical conductivity-imparting agent composed of a quaternary ammonium salt, as a technology of reducing a range of variation in electrical resistance value during continuous energization and due to changes in environmental conditions.    Patent Document 1: Japanese Patent No. 3357833 (Claims and the like)    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2002-317114 (Claims and the like)    Patent Document 3: Japanese Unexamined Patent Application Publication No. 11-140306 (Claims and the like)